You never need an argument against the use of violence, you need an argument for it. And the arguments that have been given for it are not convincing.
There is no debate about the importance of disarming Iraq and indeed other countries that have the capacity to use weapons of mass destruction. That is very important and everyone agrees on it.
Sane people do not undertake actions when they know that there is reasonable possibility that it may lead to a humanitarian catastrophe
The way to proceed with that is the way that has been done - with careful inspection procedures and efforts to ensure that the US and Britain and others will no longer carry out the policies of the past and provide Saddam with means for developing weapons of mass destruction.